Formation of the heart requires the interaction of several cell types including myocytes, fibroblasts, smooth muscle cells and endothelial cells, as well as the components of the extracellular matrix (ECM). Organization of these cellular and acellular components is necessary to respond to a variety of physiological signals in the adult. The interaction of cardiac fibroblasts with myocytes and the ECM is poorly understood and it is the main theme of the proposed studies. The specific arrangement the cellular components is critical for communication by chemical, mechanical and electrical signals. Three different models that show changes in cell number, ECM content and physiological parameters will be used to examine the hypothesis that interaction between myocytes, fibroblasts and the ECM is critical in the regulation of cardiac growth and remodeling during both normal and adaptive situations. The interaction between fibroblasts and myocytes, which is regulated by mechanical and chemical signals, is essential to the proper form and function of the heart. The specific aims that will address this hypothesis are: Specific Aim 1. Determine the effects of pressure overload hypertrophy, IL-6-loss and periostin-loss on fibroblast-myocyte interactions. The interactions of fibroblasts with myocytes and the ECM will be examined both in vivo and in vitro to determine if cell number varies with changes in the expression of cytokines (specifically IL-6) and periostin. Specific Aim 2. Determine how mechanical stimulation affects myocyte-fibroblast interactions. Using a unique 3-D culture system, the effects of mechanical signaling and cytokine stimulation will be used to measure fibroblast proliferation, apoptosis, interactions with myocytes and ECM expression. Specific Aim 3. Determine the junctional proteins and ECM receptors that regulate the interaction between fibroblasts and myocytes. These investigations will employ a variety of cellular and molecular approaches to examine cell characterization, proliferation, turnover and interaction of fibroblasts with myocytes and the ECM during normal neonatal growth, pressure overload hypertrophy and altered cardiac remodeling in periostin-/- mice and IL-6-/- mice, which display altered cardiac physiology and phenotype. Moreover, these studies will utilize a 3-D culture system that displays an in vivo-like myocyte-fibroblast-ECM phenotype. The data generated from these studies will lead to significant new information on the role of the cardiac fibroblast and its interactions with myocytes in the regulation of cardiac remodeling, as well as providing novel therapeutic targets to control the adverse affects of cardiac remodeling. PUBLIC HEALTH RELEVANCE: The proposed studies will examine the dynamic interaction between cardiac fibroblasts, myocytes and the extracellular matrix. Experimental approaches will be used to understand the chemical, mechanical and electrical signaling between these cell types and the ECM under normal growth and under pathophysiological conditions.